Google Test C ++：有没有办法读取测试中的当前控制台输出？

Question

Let us assume I have a to be tested class that has the following method:

void
MyClass::sayHello()
{
   std::cout << "Hello";
}

Now, within my google test I would like to verify that this output has been made. What would be the lastConsoleOutput equivalent be as used in my pseudo code below?

// Tests if sayHello() outputs Hello
TEST(MyClassTest, sayHello)\
{
  EXPECT_EQ(lastConsoleOutput,"Hello");
}

Thank you for any feedback!

Answer 1

In this case I would avoid redirecting or testing for values in stdout or stderr, since the access to those streams is not threads-safe in a way that output buffer may not be appended and flushed as possibly predicted.

From a testing perspective I would suggest refactoring the method to be stateless and keep the state (aka std::cout) somewhere else. In your example you start testing behavior of an external API and not the actual modification in your object.

class MyClass {

    std::sstream state;

public:

    void print(){ std::cout << state.str(); } // no need to test this method, only external API

    void changeState() {
        state << "Hello" << std::endl; // this should be tested 
    }

}

In your testing code you can now easily perform the test using

// Tests if sayHello() outputs Hello
TEST(MyClassTest, sayHello)
{
  myClass.changeState();
  EXPECT_STREQ(myClass.state.str().c_str(),"Hello");
}

Answer 2

I avoid having code like your sayHello() method. I would refactor it to something like:

void MyClass::sayHello(std::ostream& out) {
    out << "Hello";
}

Then the test method would be like this:

TEST(MyClassTest, sayHello) {
  MyClass c;
  std::stringstream strm;
  c.sayHello(strm);
  EXPECT_STREQ("Hello", strm.str.c_str());
}